X2/producer 7

Yes, you should leave SONAR 7 installed. The X2 will install in a separate directory and will pick up some of the configuration information from SONAR 7 during the install process.

well I did it and it has now caused me problems...Some plugins have now disappeared even though I can see them in the VSTplugins folder. Producer 7 has completely lost Revalver (the main reason I wanted to keep sonar 7) and X2 is not showing several plugins...any suggestions? Complete technophobe here.

Far and away the fastest way to address your issues is a call to tech support. But it is doable here too, it will just take a bit of Q&A. What OS are you running, if it is 64bit which SONAR platforms are installing. Where are looking for your VST plug-ins? Which plug-ins are not showing in X2?

It is unusual that it only involves those two plug-ins. Is it possible the name of Revalver has changed in the list? If it is in a directory under vstplugins it may show in an unexpected place in the plug-in list. The plug-in manager reports names differently than before. The TH2 installed with X2 is called TH2 Producer. You might want to take a look in the plug-in manager to verify that the plug-ins are really missing and not in an unexpected location or excluded.

Correction:  they're showing in the folder VST audio effects instead of VST instruments

Good, sorry I had to leave for a bit. If you want to use MIDI control with either Revalver or TH2 Producer, you need to:
go into the plug-in manager,
highlight the plug-in name in VST effects,
open the plug-in properties and
check "Configure as synth"
 
That has the side effect of moving the plug-in from the effects list to the synth list.

That's because Revalver and TH2 are fx not instruments. They are for processing audio signals.

Sonar 7 install. If any plug ins are missing, you can re-install Sonar 7, "minus the program files", it lets you choose all the plug ins you would want to install. I assume that is the same for X2 if you have the disc. I know that it is the same for Sonar 4. If you added them at Cakewalk, you should be able to download them again from your account.
 
I recently re-formatted my pc, and therefore went back and re-installed all the plug ins from Sonar 4 and 7, so this is an option. I did not have to install either program files for 4 and 7. However, the guy that answered set them up for synth is correct, and the other reply they are FX not instruments is also correct. TH2 Producer will show in VST Effects folder, I am not sure on Revalver. An install or upgrade should not delete any previous plug ins. But, I have read where some only work as 32 bit.
 
In your plug in manager, it is also a good idea to exclude plug ins that do not belong there, to avoid ever clicking on bad plug ins that do not work in Sonar. Just click on them, and you can drag over the list, and exclude what you don't want in there.